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924S not starting

Hello, What a great site! My first post and already begging for help!

My Daughter's 1988 924S (US) has always been very reliable transportation until this week. She drove it home and parked in the driveway one evening and the next morning it wouldn't start. It cranks over just fine, has spark at all four plugs, compression at all four cylindars, fuel pump comes on and supplies fuel to the fuel rail in the correct quanity, but she won't even try to fire.

I don't have a fuel pressure guage, so I'm not sure what the fuel pressure is, but it is high enough that when I crank the engine over the return hose will move.

I replaced the DME Relay with a new one (I checked the old one out with spare battery and multimeter and was sure it was good, but bought a new relay in frustration anywise).

All sensors have checked out ok as per the Hayes manual. Did have to adjust the throttle position sensor.

Tried removing the leads to one, then two of the injectors and still no attempt to fire.

Voltage present on the injector leads with key on is battery on one terminal and 9.96 on the other terminal. It is like this on all four injector leads as long as none are connected. Once I connect one or more of them the voltage on both terminals is battery.

I have read though all the related posts concerning starting problems and feel that my next steps should be as follows:

Check, clean all grounds.

Check fuel pressure regulator (is there a way to accomplish this without a pressure guage?)

Check pulse to injectors (will have to pick up a noid)

Open up DME and look for fried foil runs.


Any help in this matter will be greatly appreciated. Thanks to all for the excellent technical material on this site and for any help you may send my way on this post.

Old 12-10-2003, 05:37 AM
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Where did you check for spark?

What was the compression numbers?
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Hugh - So Cal 83 944 Driver Person
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When was the last time you changed your timing and balance belts and/or cam chain and tensioner?
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Old 12-10-2003, 10:17 AM
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Checked for spark by pulling all four plugs and laying them accross the intake manifold. Good spark on all four.

Compression was lower than spec. due to my not being able to warm up the engine. Numbers were all between 145 - 150.
Old 12-10-2003, 10:21 AM
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Gesh! This is a puzzel.

Define "fuel to rail in correct quanity".

How did you check this? Just watching the hose?

Any back firing?
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Hugh - So Cal 83 944 Driver Person
NOT a 'real' Porsche -- Its Better!!!!
When was the last time you changed your timing and balance belts and/or cam chain and tensioner?
New Users please add your car's year and model to your signature line!
Never break more than you fix!
Old 12-10-2003, 11:11 AM
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Took cap off end of fuel rail and placed hose over end of fitting. Cranked it over for ten seconds, multiplied the amount by 3 (30 seconds) and it was within the specs. as per the Haynes manual.

No back firing at all. Just cranks over without attempting to fire, no sputtering or anything.

Have pulled the plugs after cranking and they are dry. Seems that I can smell a light odor of gasoline after cranking it over for a while.

Timing belt is turning the distributor correctly, figure if it had just jumped a few teeth that it would start and run rough or backfire. Timing and balance shaft belts were replaced approx. 7,000 mile ago.

New clutch about 8 months ago, may be a ground problem?
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Old 12-10-2003, 11:37 AM
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Uhmmmmm you have spark..... and I would think you are getting enough fuel to at least fire if not for a few seconds.... and you have compression ....so you are left with.

Did you check that the timing marks line up?
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Old 12-10-2003, 11:45 AM
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One of the tests for failed fuel pressure regulator is to disconnect one or two of the injectors and see if the car will start.

A failed FPR will over pressure the injectors and keep them closed. By disconnecting one (or two) you give the remaining injectors full use of the shared battery current.

Another point I'm thinking of is all of the wires that go to the positive side of the battery. Clean these as well as the negative side. The injectors ground out through the DME unit and not the grounds on the back of the engine. So the ground from the battery to the chassis is critical.
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When was the last time you changed your timing and balance belts and/or cam chain and tensioner?
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Old 12-10-2003, 11:45 AM
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SoCal Driver, Thanks for your help. I am going to clean all connections on the battery and the grounds also.

I tried removing up to two injector plugs with no change.

Will charge the battery also as it has taken a beating with all the cranking and no running to charge it back up.
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Old 12-10-2003, 11:54 AM
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Might be a failed fuel pressure dampener. Keeps the fuel from the injectors. You could pull the fuel rail and lay it on the engine with some rags under it. Crank the car and see if the injectors are actually passing fuel. If not could be the FPD or just craped up injectors filter screens. You can "clean" the injector screens by blowing solvent and air back through them from the injection side.

Both are a pain to remove. Don't use the fuel rail as an anchor as you will crack it. Hold the FPR or FPD directly.
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Hugh - So Cal 83 944 Driver Person
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When was the last time you changed your timing and balance belts and/or cam chain and tensioner?
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Last edited by SoCal Driver; 12-10-2003 at 01:02 PM..
Old 12-10-2003, 12:35 PM
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If all of the injectors are not working I'm also thinking DME. You can get a noid light at most auto stores. Checks for injector pulse from the electronics.
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Hugh - So Cal 83 944 Driver Person
NOT a 'real' Porsche -- Its Better!!!!
When was the last time you changed your timing and balance belts and/or cam chain and tensioner?
New Users please add your car's year and model to your signature line!
Never break more than you fix!
Old 12-10-2003, 12:37 PM
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Picked up a noid light and I have injector pulses from the DME.

I have fuel at the fuel rail test cap in the proper amount, maybe just not enough or too much pressure. I tried removing one and then two injector leads and it still didn't attempt to start.

Did notice this afternoon that if I cranked it for longer than I should (don't want to burn up the starter) it would stumble and try to fire a little, so maybe the fuel pump check valve? FPR? FPD? Thinking I need to get a fuel pressure guage and see what I have.

Is the test fitting 16M X 1.5?
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Old 12-11-2003, 02:42 PM
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just do the ghetto test on a cold engine...

pull the rail out with the injectors still in place into a container.... crank it..

do you have fuel.
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Old 12-11-2003, 02:50 PM
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he basicaly already did that with his fuel-rail test. he needs to do the failed FPR test like Hugh described
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Old 12-11-2003, 02:54 PM
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Fuel + Air + Spark = Fire + Compression = Power

Just trying to keep things simple.

Do you have fuel to the injectors? Do you have enough? Are they Leaking? Can you hear them "clicking"?

Plenty of airflow? Checked the air filter?

You said you have spark. Do you have enough? How are the wires? Have you checked the gaps? Are they firing in the right order?

When fuel properly mixed with air is present a spark will cause it to fire.

Have you thought about timming?

Just trying to help. I find that if you keep it simple and stick to what you know you can usually figure things out.

What could have happened to it overnight that would cause it not to run? What could have happened that day to cause it to deteroirate? Were there any warnings?

Sabyre
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Old 12-11-2003, 03:08 PM
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.... a couple of posts back..... Socal asked him to lay the rail down and crank it? If you have fuel we have other problems.

If you have no fuel then get a fuel pressure gauge... It looks like FPR/fuel pump but don't assume anything.......
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Old 12-11-2003, 03:11 PM
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You can have fuel flow but little if any pressure. Or you can have too much pressure.

With the injectors injecting it seems to be a fuel flow/pressure problem.

Or???
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Hugh - So Cal 83 944 Driver Person
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When was the last time you changed your timing and balance belts and/or cam chain and tensioner?
New Users please add your car's year and model to your signature line!
Never break more than you fix!
Old 12-11-2003, 03:50 PM
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Quote:
Originally posted by SoCal Driver
With the injectors injecting it seems to be a fuel flow/pressure problem.
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Old 12-11-2003, 07:09 PM
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I've got quite similar problem.
On the way to work, car is stalled sometimes on the idle and on < 2000 rpm, but started without problems (or sometimes i did not let to stall by pushing gas). And in the evening it did not start at all. We have found that there's no pulse on injectors. Unfortunately i dont fix my car myself, so i dont know all details, but my mechanic said that after some hours of attempts to find problem it started and works fine... When i came to garage after a day it started fine. After ~5-10 minutes it tried to stall, but i was quick and pushed *gas* then it stalled after another ~5 minutes and did not start anymore.

So what i have: new injectors, new spark plugs, new wires, new fuel pump, new idle stabilizer and no pulse on injectors.

Any ideas what to check or it just rotten wires?

PS: sorry for my english.

:: 86' 924s ::
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Old 12-12-2003, 03:34 AM
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i had a car with intermitten problems,,turns out that the wireing harness lost its coating,,,and when i hit a bump, its runs like crap. then the next ,all is well,,,,,.check all wireing exposed to mother nature...
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Old 12-12-2003, 06:52 PM
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Well I really don't want to post about how I made an easy repair into a week long event, but you guys helped me out and you deserve to hear how it worked out.

A refresher: My daughter drove her 924S the night before and it was running great when she parked it. The next morning it wouldn't start. Cranked over, but wouldn't fire.

Pulled a plug then all four and had good spark.

Fuel delivery to fuel rail in correct amount (no pressure gauge)

Timing was correct.

Compression was good (145 - 150) on cold engine.

Repaced DME relay (knew it was good, replaced anyways)

All sensors checked out ok. (adjusted TPS)

Removed one/two fuel injector leads to see if problem was FPR.

Cleaned grounds.

Verified signals to injectors with noid light.

Pulled fuel rail and cranked over engine - good fuel spray at all four injectors. This really stumped me. How could I have good spark, correct timing, fuel in cylindars and good compression without the engine at least trying to start?

So I figured of all the things I checked which good indication could be easiest to mistake as being good, when in fact it wasn't.

I decided that maybe the spark I had at all four cylindars might not be hot enough. Cleaned the distributor cap inside and out. Had high resistance on center (coil) conductor. Scraped/wire brushed the conductor inside and out and the resistance was lots better.

Re-installed distributor cap and viola! Engine fired and ran perfect!

Thanks to all for the assitance, sorry I wasted your time and it turned out to be the first thing I checked!

Why does Porshce want $57 for the cap and 85 for the rotor? Why does the rotor come with the shaft instead of just being the plastic piece with lock screw?

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Old 12-14-2003, 10:11 AM
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